Rigging fabrication time for serious production and referencing
How much times is needed to build a rig like Victor from Cosmo Laundromat?


About a week or two of one_man_hours for such a rig. Depends on how good that artist is and how much he has automated with scripts.


  Does it need a big knowledge in Blender python API ?


Yes, every technical artist building rigs needs to know the API of the software, Blender or not Blender. A lot of functionality that you take as granted from Maya is not present in Blender and has to be scripted. Scripts also speed the workflow, so in production environment they are a must. The API is well documented here: https://www.blender.org/api/blender_python_api_current/

It takes about 2 months of full work time for a new technical person to become proficient in production blender rigging without prior knowledge of python, 1 month with python knowledge and slight prior experience with rigging and couple of weeks for a technical artist that transits between applications.


  Is it possible to found ressources for build it (dvd, artists)?


All resources for Blender are here: Resources for Blender

I would cheery pick as most useful the Blender Cloud (for Victor rig), Blender Cookie (good rigging tutorials), and Rigify addon (for reverse-engineering).

Also is good to know that Blender community is mainly composed of hobbyist, that don't have that much experience, and everyone is making tutorials these days. So with Blender there is a lot of free tutorials that will show you the wrong way to do things. 

An example how not to do rigging is here: http://blog.digitaltutors.com/how-to-create-your-first-character-rig-in-blender-part-1/

Also Blender develops constantly - so many tutorials are now out-of-date. 


  Is it possible like Maya to reference the model with his rig and skin into an other scene to be animated and still keeping the link between the two scene if an update is made on the rig?


Yes, this is possible but has limitations. When you link a character, you need to create a proxy of the rig, that can be edited.

When you make changes to the rig in the linked file, you have to re-create the proxy rig, and re-link it's animations. It won't happen automatically. Also the edit of the rig can easily break the animations, as everything in Blender is referenced only by names - so careful with renaming.

Also this limits the number of linked instances you can use in a scene to 1.